The present invention relates to the operation of tools above and below restrictions in a well bore and in particular, though not exclusively, to a running tool with wiper plugs used to cement casing or liner in a well bore.
In operating tools in a well bore, it is common to have to work around restrictions in the diameter of a well bore. Such restrictions may be in the diameter of casing, liner, production tubing or deployment string. Restrictions may also exist in the through bore of the work string or deployment string depending on the space requirement of the tools mounted thereon. The restrictions may be a reduction in diameter of the bore, or a convoluted path in the bore. Thus there is a need to design tools which can operate effectively above and below such restrictions.
In the field of cementing in well bores, plugs are used to separate fluids pumped through the well bore. These plugs typically comprise an elongate body terminating in a rounded nose. A number of radial wiper blades are located on the body, behind the nose. In use, the plug is inserted into the well bore and the blades contact the wall of the well bore to create a seal between those fluids in front of the plug and those behind. The plug is then moved through the well bore by the pumping of fluid behind the plug.
On reaching a reduced diameter restriction in the well bore, the plug must firstly be sized so that its nose and body can pass through the restriction and further the blades must be sufficiently flexible to fold back and reduce the overall diameter of the plug. Yet further, the blades must be suitable for correct expansion to provide a seal when the plug exits the restriction into a portion of the well bore with a wider diameter again.
A disadvantage of these plugs is that, in making the blades sufficiently flexible to fold back, the plug is prone to deviate from the central axis as it passes through the well bore above the restriction. This deviation can cause loss of contact between the blades and the wall, thus losing the required sealing function. Further the deviation can cause the nose to strike any ledge at the top of the restriction which results in the plug being stuck in the well bore. Yet further the flexible blades make ineffective contact with the walls of the well bore below the restriction.
U.S. Pat. No. 6,698,513 overcomes one of these problems by providing a second wiper plug at the base of the restriction. The second wiper plug is advantageously sized for the well bore diameter below the restriction and initially retained in position by shear pins. In use, a smaller, first or upper, wiper plug travels through the restriction and seats in the second wiper plug. Pressure build up behind the first plug causes shearing of the pins and the release of the combined wiper assembly to be pumped further down the well bore. This apparatus, however, still has the disadvantage that the wiper plug which passes through the restriction must have flexible blades. The wiper plug is thus prone to jamming above the restriction and will provide less effective wiping of the walls above the restriction also.
It is an object of at least one embodiment of the present invention to provide apparatus for use above and below a restriction in a well bore which does not require the operational part above the restriction to pass through the restriction.
It is further object of at least one embodiment of the present invention to provide a running tool wherein independent wiper plugs operate above and below the tool without the upper wiper plug passing through the tool.
It is a yet further object of at least one embodiment of the present invention to provide a method of sequentially actuating elements within a well bore where the elements are located at either side of a restriction in the well bore.